1. Chapter 49
Nervous Systems

2. Overview: Command and Control Center
The circuits in the brain are more complex than the most powerful computers.
Functional magnetic resonance imaging (MRI) can be used to construct a 3-D map of brain activity.
The vertebrate brain is organized into regions with different functions.

3. Nervous systems consist of circuits of neurons and supporting cells
The simplest animals with nervous systems, the cnidarians, have neurons arranged in nerve nets.
A nerve net is a series of interconnected nerve cells. There is no central pathway / or directional organization.
More complex animals have nerves.

4. Nerves are bundles that consist of the axons of multiple nerve cells.
Sea stars have a nerve net in each arm connected by radial nerves to a central nerve ring.

5. Nervous system organization
Eyespot
Brain
Brain
Radial
nerve
Nerve
cords
Nerve
ring
Ventral
nerve
cord
Transverse
nerve
Nerve net
Segmental
ganglia
(a) Hydra (cnidarian)
(b) Sea star (echinoderm)
(c) Planarian (flatworm)
(d) Leech (annelid)
Brain
Brain
Ganglia
Ventral
nerve cord
Anterior
nerve ring
Brain
Spinal
cord
(dorsal
nerve
cord)
Sensory
ganglia
Longitudinal
nerve cords
Figure 49.2
Ganglia
Segmental
ganglia
(e) Insect (arthropod)
(f) Chiton (mollusc)
(g) Squid (mollusc)
(h) Salamander (vertebrate)

6. Bilaterally symmetrical animals exhibit cephalization.
Cephalization is the clustering of sensory organs at the front end of the body.
Relatively simple cephalized animals, such as flatworms, have a central nervous system (CNS).
The CNS consists of a brain and longitudinal nerve cords.

7. Annelids and arthropods have segmentally arranged clusters of neurons called ganglia.
Nervous system organization usually correlates with lifestyle.
Sessile molluscs (e.g., clams and chitons) have simple systems, whereas more complex molluscs (e.g., octopuses and squids) have more sophisticated systems.

8. In vertebrates The CNS is composed of the brain and spinal cord.
The peripheral nervous system (PNS) is composed of nerves and ganglia.

9. Organization of the Vertebrate Nervous System
The spinal cord conveys information from the brain to the PNS.
The spinal cord also produces reflexes independently of the brain.
A reflex is the body’s automatic response to a stimulus.
For example, a doctor uses a mallet to trigger a knee-jerk reflex.

10. Spinal cord knee-jerk Reflex Cell body of Gray sensory neuron in
dorsal root
ganglion
Gray
matter
Quadriceps
muscle
White
matter
Hamstring
muscle
Figure 49.3 The
Spinal cord
(cross section)
Sensory neuron
Motor neuron
Interneuron

11. Invertebrates usually have a ventral nerve cord while vertebrates have a dorsal spinal cord.
The spinal cord and brain develop from the embryonic nerve cord.

12. Vertebrate Nervous System
Central nervous
system (CNS)
Peripheral nervous
system (PNS)
Brain
Cranial
nerves
Spinal cord
Ganglia
outside
CNS
Spinal
nerves
Figure 49.4 The vertebrate nervous system

13. Ventricles, gray matter, and white matter
Figure 49.5

14. The central canal of the spinal cord and the ventricles of the brain are hollow and filled with cerebrospinal fluid.
The cerebrospinal fluid is filtered from blood and functions to cushion the brain and spinal cord.

15. The brain and spinal cord contain
Gray matter, which consists of neuron cell bodies, dendrites, and unmyelinated axons.
White matter, which consists of bundles of myelinated axons.

16. Glia in the CNS Glia have numerous functions
Ependymal cells promote circulation of cerebrospinal fluid.
Microglia protect the nervous system from microorganisms.
Oligodendrocytes and Schwann cells form the myelin sheaths around axons.

17. Glia have numerous functions
Astrocytes provide structural support for neurons, regulate extracellular ions and neurotransmitters, and induce the formation of a blood-brain barrier that regulates the chemical environment of the CNS
Radial glia play a role in the embryonic development of the nervous system.

18. The Peripheral Nervous System
The PNS transmits information to and from the CNS and regulates movement and the internal environment.
In the PNS, afferent neurons transmit information to the CNS and efferent neurons transmit information away from the CNS.
Cranial nerves originate in the brain and mostly terminate in organs of the head and upper body.
Spinal nerves originate in the spinal cord and extend to parts of the body below the head.

19. peripheral nervous system
PNS
Efferent
neurons
Afferent
(sensory) neurons
Motor
system
Autonomic
nervous system
Hearing
Sympathetic
division
Parasympathetic
division
Enteric
division
Locomotion
Figure 49.7 Functional hierarchy of the
Hormone
action
Gas exchange
Circulation
Digestion

20. The PNS has two functional components: the motor system and the autonomic nervous system.
The motor system carries signals to skeletal muscles and is voluntary.
The autonomic nervous system regulates the internal environment in an involuntary manner.

21. The PNS autonomic nervous system has sympathetic, parasympathetic, and enteric divisions
The sympathetic and parasympathetic divisions have antagonistic effects on target organs.

22. The sympathetic division correlates with the “fight-or-flight” response.
The parasympathetic division promotes a return to “rest and digest.”
The enteric division controls activity of the digestive tract, pancreas, and gallbladder.

23. Promotes ejaculation and
PNS:
autonomic nervous system
Parasympathetic division
Sympathetic division
Action on target organs:
Action on target organs:
Constricts pupil
of eye
Dilates pupil
of eye
Inhibits salivary
gland secretion
Stimulates salivary
gland secretion
Sympathetic
ganglia
Constricts
bronchi in lungs
Relaxes bronchi
in lungs
Cervical
Slows heart
Accelerates heart
Stimulates activity
of stomach and
intestines
Inhibits activity
of stomach and
intestines
Thoracic
Stimulates activity
of pancreas
Inhibits activity
of pancreas
Stimulates glucose
release from liver;
inhibits gallbladder
Stimulates
gallbladder
Figure 49.8 The parasympathetic and sympathetic divisions of the
Lumbar
Stimulates
adrenal medulla
Promotes emptying
of bladder
Inhibits emptying
of bladder
Promotes erection
of genitals
Sacral
Promotes ejaculation and
vaginal contractions
Synapse

24. Table 49.1

25. The vertebrate brain is regionally specialized
All vertebrate brains develop from three embryonic regions: forebrain, midbrain, and hindbrain.
By the fifth week of human embryonic development, five brain regions have formed from the three embryonic regions.

26. Development of the human brain
Cerebrum (includes cerebral cortex, white matter,
basal nuclei)
Telencephalon
Forebrain
Diencephalon
Diencephalon (thalamus, hypothalamus, epithalamus)
Midbrain
Mesencephalon
Midbrain (part of brainstem)
Metencephalon
Pons (part of brainstem), cerebellum
Hindbrain
Myelencephalon
Medulla oblongata (part of brainstem)
Cerebrum
Diencephalon:
Mesencephalon
Hypothalamus
Metencephalon
Thalamus
Midbrain
Pineal gland
(part of epithalamus)
Hindbrain
Diencephalon
Myelencephalon
Figure 49.9
Brainstem:
Midbrain
Pons
Spinal cord
Pituitary
gland
Forebrain
Medulla
oblongata
Telencephalon
Spinal cord
Cerebellum
Central canal
(a) Embryo at 1 month
(b) Embryo at 5 weeks
(c) Adult

27. As a human brain develops further, the most profound change occurs in the forebrain, which gives rise to the cerebrum.
The outer portion of the cerebrum called the cerebral cortex surrounds much of the brain.

28. Brainstem

29. The Brainstem
The brainstem coordinates and conducts information between brain centers.
The brainstem has three parts: the midbrain, the pons, and the medulla oblongata.

30. The midbrain contains centers for receipt and integration of sensory information.
The pons regulates breathing centers in the medulla.
The medulla oblongata contains centers that control several functions including breathing, cardiovascular activity, swallowing, vomiting, and digestion.